Installation of optical fiber cables in ducts

ABSTRACT

A protective caddy for the installation of an optical fiber cable in optical fiber ducting which temporarily protects a duplex optical fiber cable assembly for an optical fiber duplex connector during insertion of the assembly into a length of ducting. The duplex optical fiber cable assembly comprises a duplex optical fiber cable and a pair of optical fiber connector sub-assemblies. The protective caddy comprises a pair of receptacles, each for receiving one of the optical fiber connector sub-assemblies. Each receptacle has a recess for protectively receiving the termination end of one of the optical fiber ferrules. In use, both the duplex optical fiber cable and the pair of optical fiber connector sub-assemblies are held to the elongate body so that the termination ends are protected by the recesses during insertion of the protective caddy and duplex optical fiber cable assembly into the length of ducting.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/696,108, filed Sep. 5, 2017, pending, which is a continuation of U.S.patent application Ser. No. 15/047,133, filed Feb. 18, 2016, now U.S.Pat. No. 9,753,234, which is a continuation of U.S. patent applicationSer. No. 14/536,013, filed Nov. 7, 2014, now U.S. Pat. No. 9,285,559.The disclosure of the prior applications is hereby incorporated byreference herein in its entirety.

BACKGROUND a. Field of the Invention

The present invention relates to the installation of an optical fibercable in optical fiber ducting, which may be an optical fiber microduct,and in particular to the installation in ducting of optical fibercabling carrying optical fibers terminated at one or more multipleoptical fiber connectors.

b. Related Art

Optical fiber connectors are used to join optical fibers where aconnect/disconnect capability is required. The basic connector unit is aconnector assembly at the end of a length of optical fiber cable, whichwill include a protective outer sheath around a coated optical fiber.The optical fiber will have an optical fiber core, and will often have aprimary coating applied to the fiber during manufacture and asurrounding secondary polymer coating. Such a coated optical fiber isreferred to as a buffered optical fiber. The buffering provides suchfunctions as mechanical isolation, protection from physical damage andfiber identification for use during installation, but the bufferedoptical fiber is itself quite delicate where this is exposed fortermination in a connector at the end of the protective outer sheath ofthe cable.

A dual connector assembly consists of two connector plugs. Due to thepolishing and tuning procedures that may be incorporated into opticalconnector manufacturing, connectors are generally assembled onto opticalfiber in a supplier's manufacturing facility. However, the assembly andpolishing operations involved can be performed in the field.

SC optical fiber connectors and LC optical fiber connectors are the mostcommon types of connectors on the market. In many data centreapplications, small connectors (e.g., LC) and multi-fiber connectors(e.g., MTP) are replacing larger, older styles of connector (e.g., SC),allowing more fiber ports per unit of rack space.

Modern connectors typically use a “physical contact” polish on the fiberand ferrule end, which usually has a slightly curved, convex surface, sothat when fibers are mated only the fiber cores touch, not thesurrounding ferrules. Some manufacturers have several grades of polishquality, for example a regular FC connector may be designated “FC/PC”(for physical contact), while “FC/SPC” and “FC/UPC” may denote “super”and “ultra” polish qualities, respectively. Higher grades of polish giveless insertion loss and lower back reflection. When a connector isterminated or assembled in the field, any damage to the polished ferruleand fiber of the connector can cause very high insertion loss.

Optical fiber cables are frequently routed in ducts. The ducts in whichoptical fiber cables are installed are usually made of cylindricalpolyethylene tubing with a diameter ranging from typically 25 mm to 100mm. Sometimes optical fiber cables are installed inside sub-ducts whichare routed inside larger ducts, such as this type of polythene tubing orducts formed in other materials, such as like concrete. Small sub-ductsare usually referred to as microducts and are often used to installsmall microduct fiber optic cables. Microducts have a size ranging fromtypically 3 mm to 16 mm and are may be installed as bundles insidelarger ducts.

The invention described below is particularly applicable to theinstallation of multiple optical fiber cabling inside microducts insidemicroducts, for example duplex optical fiber cabling, where the internaldiameter of the microduct may be less than the maximum width of themultiple optical fiber connector to be fitted at the terminated end ofthe cabling. In the context of the present invention, the term “duplex”is used to mean “dual”, “two” or “twin” fibers or assemblies, ratherthan a single fiber used for bi-directional transmission. Similarly, theterm “multiple” is used to mean “two or more”.

As will become apparent, the invention may, however, also be useful wheninstalling duplex or multiple optical fiber cabling inside larger ducts,and therefore the terms “duct” and “ducting” as used in relation to theinvention apply both to microducts and to larger ducts for routingoptical fiber cables without microducting.

One common form of optical fiber cable is the duplex optical fibercable, with one fiber being used for transmitting (Tx) and the otherfiber being used for receiving (Rx). For convenience, the duplex opticalfibers are terminated within a duplex optical fiber connector unithaving a joined pair of side-by-side connectors, each with a terminationferrule for terminating one of the optical fiber cores. The duplexoptical fibers may be held within a cable having a single outer sheathor in a cable having a pair of joined outer sheaths. Multiple duplexpairs may also be provided within one cable, each duplex pair being fortermination in one duplex connector. The invention is applicable to anysuch cable having at least one pair of optical fibers for termination ina duplex optical fiber connector, where the optical fiber cable is to beinstalled inside an optical fiber duct.

The installation of fiber optic cables in ducts can be done by pulling,in which a pre-installed thread or wire inside the duct is used to pullthe connector end of an optical fiber cable down a length of theducting. Usually, the cable being inserted into the near end of the ductis mechanically pushed at the same time. Alternatively, a techniquecalled cable jetting (also called cable blowing), can be used, togetherwith cable pushing. In cable jetting, high pressure air is blown downthe duct and the flow of air pulls along the inserted cable until thecable exits the far end of the duct.

It is not common to install a terminated fiber cable into alreadyoccupied duct because of the danger of entanglement and damage. Thespace inside the duct is normally limited by the customer's desire touse the smallest possible duct. Installing a duplex connector in a ductwould be more difficult than installing a simplex connector owing to thelarger dimensions of the duplex connector at the end of the cable. Evenin the case of the smaller LC optical fiber duplex connector, there maybe inadequate clearance inside the duct for the duplex connector whenpulling or jetting the cable down the length of ducting. There is alsothe problem that the duplex connector, or the terminated optical fiberferrules within the connector, may have to be protected from damage orcontamination during installation within the ducting, which may requireadditional protection to be fitted to or around the duplex connector,thereby potentially increasing the exterior dimensions of the connectorand making it even more difficult, or impossible, to fit the duplexconnector into the available space within the ducting.

It is an object of the invention to address these problems and toprovide a more convenient apparatus and method for installing a multipleoptical fiber connector when the optical fiber cable is to be routed ina duct for optical fiber cabling.

SUMMARY

According to a first aspect of the invention, there is provided aprotective caddy for temporarily protecting a multiple optical fibercable assembly for a multiple optical fiber connector, during insertionof said assembly into a length of ducting, said multiple optical fibercable assembly comprising a multiple optical fiber cable and a pluralityof optical fiber connector sub-assemblies, each of said sub-assembliescomprising an optical fiber ferrule having a termination end thatterminates an optical fiber extending out from said optical fiber cable,the protective caddy being in the form of an elongate body, said bodycomprising:

a first end and a second end, the first end, in use, being forwards ofsaid second end relative to the direction of insertion of said assemblyinto said length of ducting;

an axis, the axis extending between said ends; and

a first receiving portion and a second receiving portion, said portionsbeing adjacent one another along the axis whereby the first receivingportion is proximate the first end and the second receiving portion isproximate the second end; wherein the second receiving portion has anengagement feature for receiving and holding along said axis saidmultiple optical fiber cable and the first receiving portion has spacedradially around said axis a plurality of receptacles, each for receivingone of said optical fiber connector sub-assemblies, each receptaclehaving towards the first end a recess for protectively receiving saidtermination end of one of said optical fiber ferrules, whereby, in use,both the multiple optical fiber cable and the plurality of optical fiberconnector sub-assemblies are held to the elongate body so that saidtermination ends are protected by said recesses during insertion of saidprotective caddy and multiple optical fiber cable assembly into saidlength of ducting.

A multiple optical fiber connector may be composed of two or more singleoptical fiber connectors that are either joined together or heldtogether so that in use multiple optical fiber connections may be madewith a mating connector, for example a multiple optical fiber socket ora multiple optical fiber plug.

Such multiple connectors are most commonly duplex connectors formed fromtwo joined-together single optical fiber connector components.

There may be multiple such optical fiber cables, each one of which holdsat least one of the optical fibers. However, in a preferred embodimentof the invention, there is one optical fiber cable which is common toall the optical fibers, each of which is therefore held within thecommon optical fiber cable.

In a preferred embodiment of the invention, the protective caddy is fortemporarily protecting a duplex optical fiber cable assembly for anoptical fiber duplex connector, during insertion of the assembly into alength of ducting. The duplex optical fiber cable assembly thencomprises a duplex optical fiber cable and a pair of optical fiberconnector sub-assemblies, each of said sub-assemblies comprising anoptical fiber ferrule having a termination end that terminates anoptical fiber extending out from the optical fiber cable. The engagementfeature of the second receiving portion receives and holds along theaxis the duplex optical fiber cable. The first receiving portion has onopposite sides of the axis a pair of receptacles, each for receiving oneof the optical fiber connector sub-assemblies. Each receptacle then hastowards the first end, one of the recesses for protectively receivingthe termination end of one of the optical fiber ferrules. In use, boththe duplex optical fiber cable and the pair of optical fiber connectorsub-assemblies are held to the elongate body so that said terminationends are protected by the recesses during insertion of the protectivecaddy and duplex optical fiber cable assembly into the length ofducting.

In a preferred embodiment of the invention, the protective caddy issubstantially cylindrical in form with receptacles for receiving andengaging with the optical fiber cable and the optical fiber connectorsub-assemblies. As the sub-assemblies may also incorporate componentswhich are also substantially cylindrical, the assembly of thesub-assemblies and protective caddy may together present a substantiallycylindrical outer form, which will help smooth the insertion of theassembly into the ducting. Preferably, the protective caddy has arounded, bullet-like tip.

According to a second aspect of the invention, there is provided anassembly of a protective caddy and a multiple optical fiber cableassembly for a multiple optical fiber connector for insertion into alength of ducting, said multiple optical fiber cable assembly comprisinga multiple optical fiber cable and a plurality of optical fiberconnector sub-assemblies, each of said sub-assemblies comprising anoptical fiber ferrule having a termination end that terminates anoptical fiber extending out from said optical fiber cable, wherein:

the protective caddy is in the form of an elongate body, said bodycomprising:

a first end and a second end, the first end, in use, being forwards ofsaid second end relative to the direction of insertion of said assemblyinto said length of ducting;

an axis, the axis extending between said ends; and

a first receiving portion and a second receiving portion, said portionsbeing adjacent one another along the axis whereby the first receivingportion is proximate the first end and the second receiving portion isproximate the second end, the second receiving portion having anengagement feature for receiving and holding along said axis saidmultiple optical fiber cable and the first receiving portion havingspaced radially around said axis a plurality of receptacles, each forreceiving one of said optical fiber connector sub-assemblies, eachreceptacle having towards the first end a recess for protectivelyreceiving said termination end of one of said optical fiber ferrules,whereby said multiple optical fiber cable is received and held alongsaid axis by the engagement feature of the second receiving portion, andeach of said optical fiber connector sub-assemblies is received and heldwithin one of said receptacles, with the termination end of each opticalfiber ferrule being received within one of said recesses so that saidtermination ends are protected by said recesses during insertion of saidprotective caddy and multiple optical fiber cable assembly into a lengthof ducting.

According to a third aspect of the invention, there is provided a methodof using a protective caddy in the installation of a multiple opticalfiber cable assembly routed through a duct, the multiple optical fibercable assembly comprising a multiple optical fiber cable and a pluralityof optical fiber connector sub-assemblies, each of said sub-assembliescomprising an optical fiber ferrule having a termination end thatterminates an optical fiber extending out from said optical fiber cable,and the protective caddy comprising an elongate body, said bodycomprising a first end, a second end and having therein a firstreceiving portion and a second receiving portion, the first end, in use,being forwards of said second end relative to the direction of insertionof said assembly into said length of ducting, and the first receivingportion being proximate said first end and the second receiving portionbeing proximate said second end, the first receiving portion having aplurality of receptacles, each receptacle having towards the first end arecess, wherein the method comprises the steps of:

engaging said multiple optical fiber cable with the second receivingportion so that said cable is received and held by the second receivingportion along an axis extending between the first end and the second endof said body;

engaging each of said optical fiber connector sub-assemblies cable withthe first receiving portion when each of said sub-assemblies is receivedand held within a corresponding one of said receptacles, with thetermination end of each optical fiber ferrule being received within oneof said recesses so that said termination ends are protected by saidrecesses;

inserting of said protective caddy and multiple optical fiber cableassembly into a length of ducting so that said termination ends areprotected by said recesses during insertion of said protective caddy andmultiple optical fiber cable assembly into said length of ducting; and

removing said protective caddy from the multiple optical fiber cableassembly after said multiple optical fiber cable assembly has passedthrough said length of ducting.

Each of said receptacles will have an opening. Because the axis isbetween the receptacles, these openings then face away from the axis,that is, the receptacles open laterally outwards with respect to theaxis.

In a preferred embodiment of the invention, each receptacle is elongatein a direction parallel with the axis of the elongate body. Eachreceptacle then has a first end towards the first end of the elongatebody and a second end towards the second receiving portion. The recessof each of the elongate receptacles is then at the first end of each ofthe receptacles.

The main body may have a wall which separates the first receivingportion from the second receiving portion. This wall may then be at thesecond end of each of the receptacles. The wall may also have aplurality of slots that extend or cut through the wall. Each of theseslots preferably extends radially inwards from an outer periphery of thewall and provides an opening in the wall for receiving an optical fiberextending between the optical fiber cable and one of the optical fiberconnector sub-assemblies.

The elongate body may have at the first end a rounded end to aidinsertion of the protective caddy down the length of ducting.

The first end may be joined to the wall separating the receivingportions by a plurality of bands that are spaced radially around theaxis such that each receptacle is bounded by a pair of adjacent bands.In the case of a duplex optical fiber cable, when there is a pair ofbands each of these may extend on opposite sides of the axis in adirection substantially parallel with the axis.

Each of the bands may have an inwardly opposed surface that extendsalong one side of both receptacles. The bands are preferably separatefrom one another along their length so that the receptacles have anopening where these adjoin along the said axis. The bands may thenresiliently flex apart when receiving the sub-assemblies.

The bands may be joined to one another by the wall which separates thefirst receiving portion from the second receiving portion. This wall mayhave a line of weakness or a region of weakness so that the wall can bemanually broken at this weakness in order to pull the bands apart tofacilitate the release of the optical fiber connector sub-assembliesfrom the first receiving portion after insertion of the assembly intothe length of ducting.

Each of the inwardly opposed surfaces may have a concave feature forgripping the optical fiber connector sub-assembly received within one ofthe receptacles.

In a preferred embodiment of the invention, the engagement feature ofthe second receiving portion is a cylindrically shaped clip that has anopening along one side into which an optical fiber can be press-fittedto hold the cable along the axis of the elongate body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, andwith reference to the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of an optical fiber duplexconnector comprising a duplex optical fiber cable and a pair of opticalfiber connector sub-assemblies around which is assembled an outerhousing and a clamshell top and bottom cover with a quick releasemechanism;

FIGS. 2 and 3 illustrate how the optical fiber duplex connector of FIG.1 is assembled;

FIG. 4 is a perspective view of a protective caddy having a firstreceiving portion and a second receiving portion for receiving,respectively, the pair of optical fiber connector sub-assemblies and theduplex optical fiber cable

FIG. 5 shows how the protective caddy of FIG. 4 is used to protect theoptical fiber connector sub-assemblies when the duplex optical fibercable assembly is being inserted into a length of ducting;

FIG. 6 shows a top view of the assembled protective caddy and opticalfiber connector sub-assemblies and duplex optical fiber cable;

FIG. 7 is a cross section through the assembly, taken along the lineVII-VII of FIG. 6; and

FIGS. 8 to 10 show various perspective views of the protective caddyprior to use with the optical fiber connector sub-assemblies and duplexoptical fiber cable.

DETAILED DESCRIPTION OF EMBODIMENTS

A variety of optical fiber connectors are available, but SC and LCoptical fiber connectors are the most common types of connectors on themarket. The example given below relates to a dual LC optical fiberconnector that is composed of two single LC optical fiber connectors.Such connectors have cylindrical ferrules, but the person skilled in theart will recognise that the principles of the invention described belowcan be applied to other types of dual optical fiber connector includingthose that have a non-cylindrical or stepped ferrule.

FIGS. 1 to 3 show some of the components of a prior art optical fiberduplex connector 1 and also indicate how these components are puttogether to form the connector 1. The connector 1 comprises a dual LCoptical fiber connector 2 at the end of a duplex optical fiber cable 4.The dual connector 2 has a pair of identical LC optical fiber connectors6 side-by-side. Each LC connector 6 has an outer housing 8 into which isseated an optical fiber connector sub-assembly 10. Each of thesub-assemblies 10 has an elongate cylindrical optical fiber ferrule 12having at one end a termination end 14. In this example, the ferrule isof a ceramic material, although other materials may be used, as is knownin the art.

With reference now also to FIG. 7, the ferrule 12 has along its axis 16a hollow core 18 which holds and aligns an optical fiber 17, which willmost often be a single mode glass fiber. The person skilled in the artwill recognise this as a conventional arrangement, in which the fiber isterminated at the ferrule termination end 14, which is polished tominimise insertion loss when the connector is joined to a matchingoptical fiber socket (not shown). The ferrules 12 therefore eachterminate one optical fiber 17, 19 extending out from a bore 20 of theoptical fiber cable 4.

The connector 2 is mechanically joined to the cable 4 by a clamshellcover having top and bottom portions 22, 23. The top portion 22 has aquick release mechanism in the form of a flexible plate 24 which whenpressed by a user pushes down on a release lever 26 on each of the outerhousings 8. The component of FIGS. 1 to 3 are all conventional andwell-known in the art, and so will not be further described in detail.

A preferred embodiment of the invention is illustrated in FIGS. 4 to 10,which shows how a protective caddy 30 having the form of an elongatebody is used to temporarily protect a duplex optical fiber cableassembly during insertion of the assembly into a length of ducting 31,which in this example is a microduct, but which may be any other type ofducting. In this example the caddy has a one-piece elongate body.

The components of a duplex optical fiber cable assembly are indicated inFIG. 1 as those inside a dashed line 32, and comprise the pair ofoptical fiber connector sub-assemblies 10, the portion of the opticalfiber cable 4 to be inserted into the ducting 31 and the pair of opticalfibers 19 each of which extends from an end 33 of the cable 4 into oneof the sub-assemblies 10.

The duplex optical fiber cable assembly 32 is significantly smaller thanthe fully assembled connector 2 in terms of cross-sectional dimensionsrelative to an axis 34 that extends along the centre of the opticalfiber cable 4 and along a line mid-way between the side-by-sidesub-assemblies 10. Thus, the assembly 32 may be inserted into ductingwith internal dimensions too small to accept the fully assembledconnector 2. The components of the duplex optical fiber cable assembly32, particularly the termination end 14 of the ferrule 12, are delicateand could not be inserted into ducting without some sort of protection.The optical fibers 19 will normally include protective polymer claddingbut are also vulnerable to damage if bent more sharply than a minimumbend radius. The minimum acceptable bend radius depends on the type ofoptical fiber, but is of the order of 10 mm.

The optical fiber connector sub-assemblies 10 and an end-most portion 35of the cable 4 are therefore temporarily joined to protective caddy 30prior to insertion into the length of ducting 31. After the assembledcaddy 30 and duplex optical fiber cable assembly 32 has been insertedthrough the ducting, for example by pulling a line or cord 36 affixed toan aperture 37 in a rounded end 38 of the caddy at a front end 39 of thecaddy, and/or by jetting, and/or by pushing of the cable 4, the caddy 30is removed from the duplex optical fiber cable assembly 32 prior tocompleting the assembly of the connector 1 as described above.

As indicated by dot-dashed lines in FIG. 7, the protective caddyaccording to the preferred embodiment of the invention has toward thefirst end 39 a first receiving portion 41 and towards an opposite secondend 40 a second receiving portion 42. Between these ends, the first andsecond receiving portions have outermost surfaces that are substantiallycylindrical or circular about an insertion direction, such that thecaddy body 30 has an axis coincident with the cable axis 34.

The first and second receiving portions 41, 42 are adjacent one anotheralong the axis 34, being separated by a wall 43 at a rear end of thefirst portion and by a clearance gap 44 at the forwards end of thesecond receiving portion 42. The first receiving portion is thereforeproximate the first end 39 and the second receiving portion is proximatethe second end 40 of the protective caddy 30.

The first and second receiving portions 41, 42 are both preferablyelongate in form, having a length greater than the maximum diameter ofparts of the caddy 30 having these portions. The first and secondreceiving portions also match the elongate shape of, respectively, thetwo sub-assemblies 10 and the forwards cable end portion 35 so that thetwo sub-assemblies can be securely held and carried by the firstreceiving portion 41 and so that the cable end portion 35 can besecurely held and carried by the second receiving portion 42.

The second receiving portion 42 has a clip-like engagement feature forholding the duplex optical fiber cable 4, in the form of a semicircularclip or cradle 50 having substantially cylindrical inner and outer walls45, 46. The inner wall 45 has a series of circumferentially extendingridges 48 which seat within correspondingly shaped grooves 47 in theouter wall of the cable 4. These grooves 47 are a bend-limiting featureof the cable such that the cable can be bent into an arc easily untilone side of the grooves pinch together or close up, after which theforce required to further bend the cable rises sharply. Suchbend-limited tubing for an optical fiber cable is known in the art. Inthe present invention, this feature is used to secure the cable to thecaddy in an axial direction, once the internal ridges 48 of the cradleare seated within the cable grooves 47.

The first receiving portion 41 has on laterally opposite sides of the 34axis a pair of receptacles 51, 52, each for receiving one of the opticalfiber connector sub-assemblies 10. The receptacles are therefore spacedradially around the axis, or in other words, spaced circumferentiallyaround the caddy body. Each of the receptacles is a mirror image of theother, about a plane that encompasses the axis 34 of the caddy body 30.

Each receptacle 51, 52 has towards the first end 39 of the caddy body 30a recess 53 for protectively receiving the termination end 14 of one ofthe optical fiber ferrules 12. In this example, each recess is withinthe rounded end 38 and has a cylindrical inner shape which closelymatches the cylindrical outer shape of each ferrule. Each recess 53extends in a direction parallel with, and on laterally opposite sidesto, the axis 34, so that each ferrule 12 can easily slide into and outfrom each recess, with minimal clearance, in order to exclude as far aspossible any environmental contamination from reaching the ferrule ends14 once seated within the recesses 53. Behind each recess is a U-shapedchannel 54 for accepting insertion of the ferrule 12 in a lateraldirection with respect to the axis 34, and for guiding the ferrule end14 into its recess. Each U-shaped channel is dimensioned to position andhold the ferrule once inserted. This arrangement helps to avoid anycontact between the ferrule end 14 and material of the caddy body 30during insertion and removal of the ferrule from the receptacle 51, 52.

As shown most clearly in FIG. 7, the ferrule is held by a conventionalferrule holder 55 which has on a shoulder 59 a forwards surface 56 thatextends radially away from the ferrule core 18. The shoulder 56 isengaged with a ledge 57 inside each receptacle 51, 52 when thesub-assembly is seated within each receptacle. The distance in an axialdirection between the ledge 57 and a base 58 of the recess 53 is greaterthan the corresponding distance between the ferrule holder shoulder andthe ferrule termination end 14, such that a gap 49 is always providedbetween the termination end and recess base 58. This also helps toprotect the termination end from any contact damage.

As shown most clearly in FIG. 7, the rear components of each opticalfiber connector sub-assembly 10 are a ferrule holder base 60 and a coilspring 61, which together with the ferrule holder 55 form aspring-loaded ferrule carrier assembly. The ferrule holder 55 has ahollow cylindrical tubular stem 62 that extends from the shoulder 59 ina direction away from the ferrule 12, and which is concentrically seatedat forwards end of the ferrule holder base 60 within a pair of forwardlyprojecting arms 63 which have inwardly opposed part cylindrical surfaces64. The coil spring is seated between the stem 62 and part cylindricalsurfaces 64 and is retailed in an axial direction between an annularledge 65 in the ferrule holder base 60 at the base of the arms 63 and arear surface 66 of the shoulder 59 of the ferrule holder 55. The ferruleholder base 60 has a tubular rear portion 67 which supports the arms 63and which has a central bore 68 that ends from a rear end 71 of theferrule holder base to the arms 63. The bore 68 is aligned with thespace enclosed by the coil spring 61 and with a bore 69 through theferrule holder stem 62. One of the buffered optical fibers 19 extendsthrough these bores 68, 69, with the core 17 of the optical fiber seatedwithin the hollow core 18 of the ferrule 12.

Each optical fiber connector sub-assembly 10 is inserted into thecorresponding receptacle 51, 52 as follows. First the ferrule 12 isinserted forwards and at an angle to the axis 34 into the U-shapedchannel 54 and then is slid forwards until the termination end 14 beginsto enter the recess 53. At the same time, the rear part of the assembly,that is, the ferrule holder 55, ferrule holder base 60 and coil spring61, is rotated inwards in a direction towards the axis 34 until the rearpart of the assembly enters one of the receptacles 51, 52. During thisprocess, it is necessary to partially compress the spring 61, in orderto bring the ferrule holder base 60 nearer the ferrule holder 55, sothat the rearmost part of the sub-assembly 10 can fit within the lengthof the receptacle.

The ferrule holder base 60 has a pair of tapered flanges 75 on oppositeexternal side of the arms 63. These flanges are used in a one-waysnap-fit engagement of the ferrule holder base 60 inside the outerhousing 8 of the connector 6. Each of these flanges has a rearwardsfacing ledge 76. The body of the caddy 30 has an external bulge 88 inthe region of these flanges 75 to accommodate a pair of engagementfeatures 77 inside each receptacle 51, 52. The engagement features eachhave a similar shape corresponding with that of the tapered flanges, butare longer in the axial direction to allow for some axial movement ofthe ferrule holder base 60 with respect to the caddy 30 once thesub-assembly 10 is engaged in the corresponding receptacle 51, 52.

In order for the sub-assembly 10 to be fully inserted into thereceptacle 51, 52, the spring 61 must be compressed by the right amountfor each of the tapered flanges 75 to enter the corresponding engagementfeature 77. The spring 61 tends to expand once this engagement is made,pushing the rear end 71 of the ferrule holder base towards a rear endsurface 72 of the receptacle, while at the same time ensuring a positivecontact force between the shoulder 56 of the ferrule holder 55 and theledge 57 inside each receptacle. The rear end surface 72 of thereceptacle is the forward surface of the wall 43, and before the rearend 71 of the ferrule holder base contacts this surface 72, rearwardsmovement of the ferrule holder base 60 is stopped by contact of therearwards facing ledge 76 of each tapered flange 75 with a correspondingforwards ledge 78 of each engagement feature 77. This arrangementensures a small gap 79 remains between the rear end 71 of the ferruleholder base 60 and the wall forwards surface 72, which helps to protectthe optical fiber 19 from sharp changes in direction at this point andwhich is also useful in providing a feature of the sub-assembly to begripped by a tool when the sub-assembly is to be removed from thereceptacle.

This arrangement, in which the engagement features 77 must be alignedwith the tapered flanges 75, also helps to prevent over-compression ofthe spring during insertion or removal of the sub-assemblies 10 from thereceptacles 51, 52.

The invention therefore preferably includes an engagement feature withineach receptacle to position each sub-assembly in a longitudinalorientation in which a spring-loaded ferrule carrier assembly is seatedwith a rearmost surface of the assembly free from contact with asupporting surface and with the termination ferrule positively engagedwithin its recess.

The wall 43 has a pair of slots 73, one for each receptacle 51, 52. Inthis example, the slots open laterally outwards in opposite directionsand are V-shaped, in order to guide the buffered optical fiber 19 intothe optimal alignment with the bore 68 in the ferrule holder base 60 andthe bore 20 in the optical fiber cable 4.

As can be seen most clearly from FIG. 5, the purpose of the clearancegap 44 is to provide space for the buffered optical fibers 19 to berouted between the sub-assemblies 10 and the cable 4 in an orientationand spacing similar to, but not identical with, the orientation of thesecomponents in the fully assembled connector 1. In particular, it isimportant that the orientation of the buffered optical fibers remains asstraight as possible both during the joining of the duplex optical fibercable assembly 32 to the caddy 30 and during the final separation of thecaddy from the assembly 32 after the inserting through the ducting 31.For this reason, in order to minimise bending of the optical fiber 19,the part of the clip or cradle 50 nearest the slot 73 may, as shown bythe dashed line 85 in FIG. 4, be cut away or chamfered to provideadditional space for the movement of the buffered optical fiber 19.

Each receptacle 51, 52 is therefore a laterally accessible pocket in thefirst portion 41 of the caddy 30. Each receptacle has opposite sidebands or walls 81, 82 extending from the rear surface 72 of thereceptacle to the ledge 57 against which the ferrule holder 55 isseated. As shown most clearly in FIGS. 8 to 9, these side walls have acylindrical central portion 80 running the length of the walls, eitherside of which is an inner lip 83 and an outer lip 84. These features ofthe cylindrical central portion 80 and inner and outer lips 83, 84 arecontinuous in a longitudinal direction, except where these are broken bythe longitudinal engagement feature 77 where this extends laterallyinside each recess 51, 52. Although only one wall 81 is shown fully inthe drawings, the other wall 82 is a mirror image.

The inner lip 83 of each receptacle abuts the inner lip of the otherreceptacle along its most of its length so that there is an opening 86between the receptacles 51, 52. The opening allows the sub-assemblies 10to be inserted so that they are in contact, or nearly in contact, i.e.back-to-back, which minimises any wasted space in a lateral directionbetween the seated sub-assemblies 10. This therefore minimises thelateral extent of the caddy body 30 in this direction.

The arrangement of protective caddy described in detail above istherefore in the form of compartmentalised protective carrier or holder30, and could be described as being a laterally segmented protectiveholder 30, for protecting a pair of optical fiber connectorsub-assemblies of a duplex optical fiber cable.

The ferrule holder has an external dimension which just passes betweenthe outer lips 84 with minimal clearance. The ferrule holder base 60,including tapered flanges 75, may be slightly larger than the distancebetween the opposed outer lips 84.

The material of the main body of the caddy 30 is preferably a plasticsmaterial, for example polypropylene, with the elongate body 30 beingformed in an injection moulding process. In the preferred embodiment ofthe invention, the elongate body is resiliently flexible so that theferrule holder base 60, including tapered flanges 75, can push apart thebands or walls 81, 82 in a central portion of the receptacle 51, 52sufficiently so that the sub-assembly is received securely within thereceptacle when the walls 81 relax after passage of the sub-assemblyinto the receptacle. The sub-assembly is then seated in the opposedlongitudinal grooves.

The invention therefore preferably provides an arrangement in which thesub-assembly is temporarily secured within its receptacle in a press-fitengagement in which the receptacle resiliently deforms to accept thesub-assembly.

It should be noted that the ability of the receptacle walls to flex toallow passage of the sub-assembly into and out from each receptacleresults not just from the choice of materials, but also from thepresence of the opening 86 between the receptacles 51, 52 which permitsthe bands 81, 82 to flex. The opening therefore not only saves space,but provides a useful function in the temporary securing of thesub-assemblies 10 within the receptacle 51, 52.

The arrangement described above protects both the duplex optical fibercable 4 and the pair of optical fiber connector sub-assemblies 10, andparticularly the termination ends 14, during insertion of the protectivecaddy 30 and duplex optical fiber cable assembly 32 into the length ofducting 31.

As mentioned above, after the caddy 30 and duplex optical fiber cableassembly 32 have been fully inserted through the ducting 31, theprotective caddy is removed from the duplex optical fiber cableassembly, after which the assembly of the optical fiber duplex connectorincorporating the duplex optical fiber cable assembly is completed.

To facilitate removal of the protective caddy from the duplex opticalfiber cable assembly, the caddy may, optionally, include a relativelyweakened line or region adapted to be broken. FIG. 10 shows how thecaddy 30 may be modified to create such a weakened line or region, byremoving most of the material between the slots as indicated bycross-hatching indicated with numeral 90. A tool may then be used toprise apart of the top and bottom walls 81, 82 where these are joined bythe wall 43 at the rear of the receptacles 51, 52. The top wall, whichis not joined directly to the second receiving portion 42, may then bebent upwards and optionally broken off at a forwards end where this isjoined to the rounded end 38, thereby allowing easy removal of thesub-assemblies 10, optical fibers 17, 19 and optical fiber cable 4 fromthe protective caddy 30. The invention therefore also extends to aprotective caddy having a breakable elongate body 81, 90 to facilitatefreeing the optical fiber connector sub-assemblies 10 from engagementwith the first receiving portion 41.

The preferred embodiments described in detail above have a left/rightsymmetry for the receptacles, such that the cross-section through thereceptacles is the same if rotated by 180° about the axis of theelongate protective caddy.

From this it can be seen that although the arrangement described aboverelates to a duplex optical fiber cable assembly, the principles of theinvention can be applied to an optical fiber cable assembly having morethan two optical fibers, each with its own optical fiber connectorsub-assembly. For example, an optical fiber cable assembly having threeoptical fibers and three corresponding optical fiber connectorsub-assemblies can be secured using a protective caddy having threereceptacles, each for receiving one of the optical fiber connectorsub-assemblies. These receptacles can be spaced radially around thecaddy axis so that in cross-section there is a triangular symmetry tothe receptacles, such that the cross-section is the same if rotated by120° about the axis.

In the case of a protective caddy for temporarily protecting a multipleoptical fiber cable assembly having four optical fibers, there would bea square symmetry to the receptacles, such that the cross-section is thesame if rotated by 90° about the axis.

Although there will be a limit to number of optical fibers which canusefully be combined into a single cable or connected to a multipleoptical fiber connector, the person of ordinary skill in the art willsee that the protective caddy can be adapted for use with any practicalnumber of optical fiber connector sub-assemblies.

The invention described above therefore provides a convenient apparatusand method for installing a multiple optical fiber connector when theoptical fiber cable is to be routed in a duct for optical fiber cabling.

It is to be recognized that various alterations, modifications, and/oradditions may be introduced into the constructions and arrangements ofparts described above without departing from the spirit or scope of thepresent invention, as defined by the appended claims.

What is claimed is:
 1. A protective caddy for temporarily protecting amultiple optical fiber cable assembly for a multiple optical fiberconnector, during insertion of said assembly into a length of ducting,said multiple optical fiber cable assembly comprising a multiple opticalfiber cable and a plurality of optical fiber connector sub-assemblies,each of said sub-assemblies comprising an optical fiber ferrule having atermination end that terminates an optical fiber extending out from saidoptical fiber cable, the protective caddy being in the form of anelongate body, said body comprising: a first end and a second end, thefirst end, in use, being forwards of said second end relative to thedirection of insertion of said assembly into said length of ducting; anaxis, the axis extending between said ends; and a first receivingportion and a second receiving portion, said portions being adjacent oneanother along the axis whereby the first receiving portion is proximatethe first end and the second receiving portion is proximate the secondend; wherein the second receiving portion has an engagement feature forreceiving and holding along said axis said multiple optical fiber cableand the first receiving portion has spaced radially around said axis aplurality of receptacles, each for receiving one of said optical fiberconnector sub-assemblies, each receptacle having towards the first end arecess for protectively receiving said termination end of one of saidoptical fiber ferrules, whereby, in use, both the multiple optical fibercable and the plurality of optical fiber connector sub-assemblies areheld to the elongate body so that said termination ends are protected bysaid recesses during insertion of said protective caddy and multipleoptical fiber cable assembly into said length of ducting.
 2. Aprotective caddy as claimed in claim 1, in which the protective caddy isfor temporarily protecting a duplex optical fiber cable assembly for anoptical fiber duplex connector, during insertion of said assembly into alength of ducting, said duplex optical fiber cable assembly comprising aduplex optical fiber cable and a pair of optical fiber connectorsub-assemblies, each of said sub-assemblies comprising an optical fiberferrule having a termination end that terminates an optical fiberextending out from said optical fiber cable, wherein the engagementfeature of the second receiving portion is for receiving and holdingalong said axis said duplex optical fiber cable and the first receivingportion has on opposite sides of said axis a pair of said receptacles,each for receiving one of said optical fiber connector sub-assemblies,each receptacle having towards the first end one of said recesses forprotectively receiving said termination end of one of said optical fiberferrules, whereby, in use, both the duplex optical fiber cable and thepair of optical fiber connector sub-assemblies are held to the elongatebody so that said termination ends are protected by said recesses duringinsertion of said protective caddy and duplex optical fiber cableassembly into said length of ducting.
 3. A protective caddy as claimedin claim 1, in which each of said receptacles has an opening and saidopenings face away from said axis.
 4. A protective caddy as claimed inclaim 1, in which said receptacles open laterally outwards with respectto said axis.
 5. A protective caddy as claimed in claim 1, in which eachreceptacle is elongate in a direction parallel with said axis, eachreceptacle having a first end towards the first end of the elongate bodyand a second end towards the second receiving portion, the recess ofeach of said elongate receptacles being at the first end of each of saidreceptacles.
 6. A protective caddy as claimed in claim 1, in which themain body has a wall which separates the first receiving portion fromthe second receiving portion.
 7. A protective caddy as claimed in claim5, in which the main body has wall which separates the first receivingportion from the second receiving portion, said wall being at the secondend of each of said receptacles.
 8. A protective caddy as claimed inclaim 6, in which said wall has a plurality of slots therein, each ofsaid slots extending radially inwards and providing an opening in saidwall for receiving one of said optical fibers extending between saidoptical fiber cable and one of said optical fiber connectorsub-assemblies.
 9. A protective caddy as claimed in claim 6, in whichsaid first end of the elongate body is joined to said wall by aplurality of bands, said bands being spaced radially around said axissuch that each receptacle is bounded by a pair of adjacent bands.
 10. Aprotective caddy as claimed in claim 2, in which the main body has awall which separates the first receiving portion from the secondreceiving portion and said first end of the elongate body is joined tosaid wall by a pair of bands, said bands extending on opposite sides ofsaid axis such that each receptacle is bounded by said bands.
 11. Aprotective caddy as claimed in claim 10, in which each of said bands hasan inwardly opposed surface that extends along one side of bothreceptacles.
 12. A protective caddy as claimed in claim 11, in whichsaid bands are separate from one another so that said receptacles havean opening therebetween along said axis.
 13. A protective caddy asclaimed in claim 12, in which said bands are joined to one another bythe wall which separates the first receiving portion from the secondreceiving portion, said wall having a line of weakness or a region ofweakness so that said wall can be broken in order to pull apart saidbands to facilitate the release of the optical fiber connectorsub-assemblies from the first receiving portion after insertion of saidassembly into said length of ducting.
 14. A protective caddy as claimedin claim 9, in which each of said inwardly opposed surfaces has aconcave feature for gripping said optical fiber connector sub-assemblyreceived within one of said receptacles.
 15. A protective caddy asclaimed in claim 1, in which the first end of the elongate body is arounded end.
 16. A protective caddy as claimed in claim 15, in whichsaid recesses are provided within said rounded end.
 17. A protectivecaddy as claimed in claim 1, in which each receptacle has a portionnearest each receptacle with a U-shape for receiving and holding one ofsaid optical fiber ferrules.
 18. A protective caddy as claimed in claim1, in which the engagement feature of the second receiving portion is acylindrically shaped clip, said clip having an opening along one sideinto which an optical fiber can be press-fitted to hold said cable alongsaid axis.
 19. A protective caddy as claimed in claim 18, in which saidclip has at least one ridge therein extending in a circumferentialdirection for engaging with a groove in an external surface of saidoptical fiber cable.
 20. An assembly of a protective caddy and amultiple optical fiber cable assembly for a multiple optical fiberconnector for insertion into a length of ducting, said multiple opticalfiber cable assembly comprising a multiple optical fiber cable and aplurality of optical fiber connector sub-assemblies, each of saidsub-assemblies comprising an optical fiber ferrule having a terminationend that terminates an optical fiber extending out from said opticalfiber cable, wherein: the protective caddy is in the form of an elongatebody, said body comprising: a first end and a second end, the first end,in use, being forwards of said second end relative to the direction ofinsertion of said assembly into said length of ducting; an axis, theaxis extending between said ends; and a first receiving portion and asecond receiving portion, said portions being adjacent one another alongthe axis whereby the first receiving portion is proximate the first endand the second receiving portion is proximate the second end, the secondreceiving portion having an engagement feature for receiving and holdingalong said axis said multiple optical fiber cable and the firstreceiving portion having spaced radially around said axis a plurality ofreceptacles, each for receiving one of said optical fiber connectorsub-assemblies, each receptacle having towards the first end a recessfor protectively receiving said termination end of one of said opticalfiber ferrules, whereby said multiple optical fiber cable is receivedand held along said axis by the engagement feature of the secondreceiving portion, and each of said optical fiber connectorsub-assemblies is received and held within one of said receptacles, withthe termination end of each optical fiber ferrule being received withinone of said recesses so that said termination ends are protected by saidrecesses during insertion of said protective caddy and multiple opticalfiber cable assembly into a length of ducting.